This invention relates in general to apparatus for manufacturing color cathode ray tubes and in particular to apparatus for automatically controlling the intensity of the light source employed for screening the face panel of a color picture tube.
In a conventional tri-color cathode ray tube the luminescent screen formed on the target surface of the face panel comprises a myriad of interleaved phosphor elements. Actually, the phosphor elements are relegated to one of three groups with all the phosphors in an assigned group selected to emit, upon excitation, one of the three primary colors, i.e., red, green or blue. In practice, all the elements of one color group are developed in one operation, which operation is then repeated for each of the other colors. The actual process by which these phosphors are applied to the face panel involves photographic techniques which are well known and understood in the art.
A new generation of color reproducing cathode ray tubes recently introduced utilizes a graded aperture mask in conjunction with a screen construction in which the phosphor elements are separated by deposits of a light absorbing material comprising a black pigment. A tube of this type is described in U.S. Pat. No. 3,146,368 which issued to Joseph P. Fiore et al. on Aug. 25, 1964. In view of this screen arrangement, such a tube has come to be designated a black-surround color tube.
It is extremely important in processing a black-surround picture tube that the openings in the black surround material not only be accurately dimensioned in accordance with a predetermined grade but also that the phosphor deposits within any triad be uniform across the target surface. To this end a process which facilitates achieving these requirements contemplates the following procedure. First, the target surface of the face panel is coated with clear pva (polyvinyl alcohol), a material which is rendered insoluble when exposed to light. This sensitized surface is then subjected to multiple exposures of actinic energy, either successively, or simultaneously, from sources having locations corresponding to the color centers subsequently used for exposing the color phosphors. The pva coated panel now registers a myriad of latent images corresponding to the positions to be occupied by the three groups of phosphor dots. The panel is then washed with water to remove the unexposed pva material, thus leaving a target surface comprised of a myriad of pva dots. The next step is to coat the entire surface of the target area with a graphite solution, for example, "Aquadag", a material available from Acheson Colloids of Port Huron, Mich. The coated panel is then heated to dry the Aquadag material. Then, the target surface of the panel is treated with a solution of peroxide which dissolves the pva dots. Since the Aquadag material is not soluble in peroxide only the pva dots are dissolved. The panel is washed again, this time to remove the dissolved pva so that the target surface of the panel now constitutes a black grille having a myriad of openings for receiving the red, green and blue phosphor materials.
The processing procedure above described must be closely monitored in order that the size and configuration of the pva dots be uniform. This precaution must be taken since these dots ultimately define the recesses in the black surround material that receive the phosphors. The dimensions of the pva dots are determined by the mask apertures, exposure time and also the intensity of the light impinging upon the pva coated target. Mask aperture size and exposure time are relatively easy to control. However, maintaining a constant level of light intensity from the actinic energy source is not so readily achieved because of the influence of such factors as line voltage, lighthouse lamp aging, etc. Accordingly, control of the intensity of the emanations from the light source is of particular concern where uniformity of the latent images is required, as is particularly the case presented in processing a black-surround type color picture tube.
It is therefore a general object of the invention to provide apparatus for accurately processing the light absorbing layer applied to the target surface of a black-surround type color picture tube.
It is a specific object of the invention to provide apparatus for automatically maintaining the output of a source of actinic energy at a predetermined level.
Apparatus for automatically maintaining, at a predetermined level, the output of a source of actinic energy employed for exposing a radiant energy sensitive coating deposited upon the target surface of a cathode ray tube face panel comprises a chamber for supporting the face panel and a source of actinic energy located in the chamber and disposed in a confronting relation to the target surface for irradiating the coating deposited thereon. The apparatus also comprises means, including an adjustable controller, for energizing the source. The light energy translating means is disposed adjacent the energy source, but outside the irradiation path between the source and the target surface, for monitoring the radiant energy output of the source. Means, coupled to the light energy translating means and responsive to the energy translated therethrough, derives a control signal representative of the instantaneous energy level of the energy source. Finally, means, responsive to the control signal, are provided for actuating the controller to maintain the output of the energy source at a predetermined level.